Automatic test equipment (ATE) have become well known in the art. These systems are used with a variety of applications, including aerospace, semiconductor processing and automotive systems. A typical ATE device comprises a controller to methodically operate an apparatus (such as a jet engine control system) so that sensors measure one or more parametric values generated by the apparatus. The results of the test can then be viewed by the operator or stored in an associated memory for later analysis.
Automatic test equipment in general are not adapted for use in diagnosing malfunctioning systems. Consequently, field service personnel have been limited to the use of manuals designed and written by an expert troubleshooter to aid in the determination of faults for that particular apparatus. As automotive, electronic and aircraft systems have increased in complexity, so have the problems associated with accurately and economically troubleshooting malfunctioning components.
An example of diagnostic equipment for use in troubleshooting systems includes the automotive vehicle trouble checking apparatus disclosed in U.S. Pat. No. 4,839,811. The '811 apparatus is used with an automobile having sensors providing signals indicative of the various engine parameters. The apparatus includes a control circuit responsive to the sensor signals for calculating a value corresponding to a setting of each of a plurality of means for controlling the automotive vehicle. A self-checking unit is connected to the control circuit for checking sensor signals applied to the control circuit to provide a self-checking code indicative of the cause of automotive vehicle trouble when at least one of the sensor signals generates an abnormal value. The external trouble checking unit is connected through a detachable connector to the self-checking unit for utilizing the sensor signals fed to the control circuit and the self-checking code to find a cause of the automotive trouble. The '811 apparatus allows the incorporation of a knowledge database of known parameters along with a logic to allow first order analysis of the sensed signals.
Japanese Patent No. 62-6857 discloses another fault diagnostic apparatus for use with vehicles. The system includes a plurality of predicting systems including forward, rearward and inquiring systems through a selecting means. The system predicts the causes of the sensed fault on the basis of symptom information in accordance with the selected predicting system.
The current generation of airplane electronic engine control (EEC) systems are more sophisticated than aircraft control systems of the prior art and are substantially more elaborate than those which are found in other applications, such as in automobiles. These systems include redundant sensors and control system componentry as part of the overall aircraft EEC system. The enhanced control features of these EEC systems result in a more complicated system with correspondingly more complex diagnostic procedures which must be followed to properly troubleshoot a malfunction. This increased complexity places still higher demands on the quality of the service technician, as problems must be addressed in an ever more rigorous and systematic manner that require higher levels of skill and extraordinary discipline.
In recent years "expert systems" have been developed as an analysis aid for a variety of applications. These expert systems are computer based systems characterized by a set of user defined rules and facts stored in a knowledge database, as well as a software user interface. An "inference engine" is included that processes these rules and facts to conclude new facts and rules. The inference engine can prompt a technician for additional information to aid in the troubleshooting process.
An example of a device incorporating an expert system is the portable maintenance aid (PMA) offered by the Grumman Corporation. The PMA attempts to provide the technician with a digitized version of the troubleshooting manual whose access is aided and controlled by an expert system. The troubleshooting manual is written and placed in digital form in a computer. The Grumman PMA receives a series of inputs from the maintenance technician and responds with corresponding series of excerpts from the manual.
Known maintenance aid systems of this type are more appropriately characterized as "interactive electronic publications", since the expert system is utilized as an aid in stepping the maintenance technician through the complicated electronic manuals at an increased speed to reduce troubleshooting time. That is, the expert system reorders the maintenance manual on the basis of questions to and answers from the technician to provide a more efficient path to isolate the problem.
In view of the above, it would be advantageous to have a diagnostic system adapted for use with troubleshooting aircraft engine systems that would be able to be used by a technician having minimum skill and which could tolerate mistakes made thereby and yet would allow for economical and accurate diagnosis of defective components. The present invention is drawn towards such a system.